1. Field of the Invention
The present invention relates to an image reading device for a digital copier, a scanner, a facsimile, and the like and an image forming apparatus that employs the image reading device.
2. Description of the Related Art
The TWAIN is known as one of technical standards for connecting an image input device such as a scanner, a digital camera, and the like to a personal computer, which means that, if a device is compatible with the TWAIN, an image can be input from all application softwares that are compatible with the TWAIN.
Technologies related to an image reading device are disclosed in, for example, Japanese Patent Publication No. 3553363 and Japanese Patent Application Laid-open No. H11-136454. A digital image reading device, which is disclosed in Japanese Patent Publication No. 3553363, irradiates and reads a standard plate and carries out shading correction. In the digital image reading device, a predetermined speed priority mode and a predetermined image quality priority mode can be randomly set for an image reading operation. Upon completion of a string of the image reading operation, the digital image reading device irradiates and reads the standard plate, and if the next image reading operation is set to the speed priority mode mentioned earlier, the digital image reading device uses shading correction values that use the previously read data. If the next image reading operation is set to the image quality priority mode mentioned earlier, the digital image reading device again irradiates and reads the standard plate before start of the image reading operation and uses the shading correction values that use the obtained read data.
In the invention disclosed in Japanese Patent Application Laid-open No. H11-136454, a read scanner and a read control unit are included for enhancing efficiency of a repeated copying operation and for ensuring that a writing position, when repeatedly reading the same original during reading of a color original, on a photosensitive drum is aligned in time. During a string of the image reading operation, the read scanner scans the original and reads an image. At the time of initial reading of a string of the image reading operation, the read control unit causes the read scanner to start reading from a first position. From the second reading onwards, the read control unit causes the read scanner to start reading from a second position that is nearer to a position of the original than the first position. Upon completion of the string of the image reading operation, the read control unit returns the read scanner to the first position.
In the invention disclosed in Japanese Patent Publication No. 3553363, at the time of reading in the speed priority (black and white (B&W)) mode, shading correction is executed based on a standard white plate data that is read after the previous reading operation. At the time of reading in the image quality priority (color) mode, the standard white plate data is again read before reading the original to execute the shading correction. Thus, when reading in the speed priority mode, productivity is enhanced by tacitly accepting image quality deterioration.
However, when reading in the speed priority mode, a time before using the standard white plate data, which is read after the previous reading operation, is not clearly known. According to Japanese Patent Publication No. 3553363, the shading correction values do not change significantly in a short time. However, an actual lamp luminance includes temperature characteristics. For example, in a xenon lamp that is widely used currently, a difference between lamp temperatures at the time of luminescence is ten percent. In other words, illuminance when the lamp is hot and when the lamp is cold differs by approximately ten percent. If the shading correction values increase by ten percent, the corrected original data becomes darker by ten percent. Due to this, a white patch of the original is likely to become data that is black textured and that includes significant noise.
Further, for increasing the productivity of continuous reading, many of the currently used scanners use a sheet through (hereinafter, “DF”) reading mode in which a sheet shaped original is moved and image data is read by a stopped optical system. In DF reading for copying, reading can be executed by subsequently moving the originals based on an internal timing of the scanner. However, when reading using the TWAIN, the reading operation needs to be completed for each page. Further, because read data is uploaded on a network, the reading operation depends on a use environment. Due to this, a command to start reading the next original is delayed. Thus, productivity when using the TWAIN is lower compared to the productivity in the DF reading mode for copying.
Upon completion of reading one original or a string of the originals, the lamp of the scanner is switched off as a sequence at the time of completion. Even if a read start request is issued after the sequence mentioned earlier, the scanner cannot start reading immediately and reading is started only after a waiting time until the lamp is switched on and a light amount has stabilized. Due to this, the productivity when reading using the TWAIN is further reduced.
FIGS. 1A and 1B are flowcharts of a representative operation of the existing scanner. In the existing scanner, an illumination lamp is switched on when scanning starts (Step S101) and whether a reading mode is a color mode or a black and white (B&W) mode is checked (Step S102). Next, operation settings are carried out according to the reading mode (the color mode or the B&W mode). Settings, which differ according to the reading mode such as setting of a line period, setting of an amplification factor that amplifies a charge coupled device (CCD) output and the like, are carried out (Step S103). Next, the scanner checks whether the reading mode is the DF mode or a book mode (Step S104). If the reading mode is the DF mode, the scanner executes a subsequent process after Step S105. If the reading mode is the book mode, the scanner executes a process of the book mode. The book mode indicates a reading mode in which the original, especially a thick book, is placed on a contact glass and the original is read by moving the scanner in a sub-scanning direction. However, because the book mode is not treated as a target in the present invention, an explanation is omitted.
If the reading mode is the DF mode, the scanner carries out setting operations for a DF mode read setting (Step S105), a DF scan motor drive setting (Step S106), a black level detection (Step S107), and setting of an interline correction amount for white plate reading (Step S108). Next, the scanner drives a stepping motor (Step S109), and reads the standard white plate to retrieve shading data while shuttling a carriage between an original reading position (hereinafter, also referred to as “a home position (HP)”) and the standard white plate (Step S110). Next, the scanner sets the interline correction amount for reading the original (Step S111) and stops the carriage at the home position, thus enabling reading of the original, and reads the original using the DF (Step S112). Next, the scanner checks whether a read request has been issued (Step S113).
At Steps S105 and S106, the scanner carries out the operation settings that are compatible with the DF reading mode. The operation settings include a gray balance adjustment for deciding a dynamic range of reading and an output balance of red, green, and blue (RGB). Further, the scanner also sets a stepping motor driving pattern for shuttling the carriage between the standard white plate and the HP.
During the black level detection at Step S107, the scanner reads a black level that becomes a standard level of the image data. The scanner sets at Step S108, the interline correction amount that is an interline correction amount for reading the standard white plate. In other words, because an RGB sensor of a CCD is physically positioned towards the sub-scanning direction, the interline correction amount indicates a data delay amount that delays data that is read temporally earlier, thus aligning RGB data. Setting of the interline correction amount at Step S111 is similar to the data delay amount that is processed at Step S108 for reading the original.
If the read request has been issued at Step S113, the process returns to Step S107 and the scanner carries out the reading operation of the next original. If the read request has not been issued, the scanner waits until lapse of 2500 milliseconds (ms) after completion of reading of the original and checks whether a read request has been issued (Step S115). If the read request is issued within the waiting time mentioned earlier, the process returns to Step S102 and the scanner carries out the next reading operation. Upon lapse of 2500 ms from the completion of reading of the original, in other words, upon completion of the waiting time (Yes at Step S114), the scanner switches off the illumination lamp (Step S116), thus ending the process.
Such a control is carried out for avoiding a reduction in the productivity. In the example shown in FIGS. 1A and 1B, the scanner is controlled such that a margin of a predetermined time (2500 ms at Step S114) is allocated and the scanner waits without switching off the illumination lamp within the predetermined time. If the read request is issued within the predetermined time, the scanner can carry out scanning immediately. The waiting time mentioned earlier is merely an example, and the waiting time can be appropriately set according to the functions and use of a device.
However, due to the control mentioned earlier, because the illumination lamp is always switched on during the predetermined time, a life of the illumination lamp is reduced.